A study of an optical signal transmission technology for increasing a bandwidth is being pushed ahead as a method for realizing a high capacity for an optical network system that enables high-capacity data communications. For example, an increase in the bandwidth can be achieved by transmitting (unless otherwise limited, including exchanging and transferring) a signal after a signal having a low bit rate is contained into a frame of a high speed signal having a higher bit rate than that or by increasing a bit rate of a signal having a given bit rate to a higher speed.
The conventional optical network system forms a wavelength division multiplexing (WDM) network, and includes a plurality of WDM devices as optical transmission devices including a bit rate adjustment function.
Those WDM devices employ a WDM transmission technology conforming to ITU-T G.709/Y.1331: Interfaces for the Optical Transport Network (OTN) and ITU-T G.7044/Y.1347: Hitless Adjustment of ODUflex (GFP)(HAO) recommended by International Telecommunications Union-Telecommunication Standardization Sector (ITU-T).
A plurality of optical wavelength paths are set among those WDM devices, and a first signal transferring frame is transmitted through those optical wavelength paths. Data (client signal) output from a client device is input to the WDM device, and is contained into a second signal transferring frame having a lower bit rate than the first signal transferring frame. Further, this data is transmitted to the client device corresponding to a desired destination after being contained into a time slot (TS) allocated thereto within the first signal transferring frame.
In this optical network system, the bit rate of the second signal transferring frame is determined based on the bit rate of the data, and when the data is contained into the first signal transferring frame, a number of time slots allocated thereto is determined.
There already exists a technology for changing the bit rate of the second signal transferring frame containing the data and the number of time slots of the first signal transferring frame depending on a change of the bit rate of the data changes without giving an error to the data.
Examples of the signal transferring frame include an optical channel transport unit (OTU) frame and an optical channel data unit (ODU) frame that are recommended by ITU-T G.709/Y.1331. Further, an example of the technology for changing the bandwidth (bit rate) of the signal transferring frame containing the data and the number of time slots thereof without giving an error to the data is recommended by ITU-T G.7044/Y.1347.
The following are related arts to the invention.    [Non-patent document 1] ITU-T G.709/Y.1331: Interfaces for the Optical Transport Network (OTN)    [Non-patent document 2] ITU-T G.7041/Y.1303: Generic framing procedure (GFP)    [Non-patent document 3] ITU-T G.7044/Y.1347: Hitless Adjustment of ODUflex (GFP)(HAO)    [Non-patent document 4] ITU-T G.872: Architecture of optical transport networks